As a group of security staff circled, they held the jagged plastic out, threatening their pursuers to back off.

Eventually the duo was able to make their way out of the unit where they were being held and ran off into the countryside.

They had escaped from a secure mental health facility in the UK. One of them was an Irish boy. It would be three days before he was found and returned to his unit.

On another occasion riot police were summoned after he and another minor again fashioned makeshift weapons and began smashing light fittings.

These are just two of the dozens of shocking episodes that have bookmarked the life of PA, the initials under which he is referred to in court papers about his case.

PA isn’t being detained as a criminal. Although he has committed crimes, he is not being held for any of these.

His detention has instead occurred by virtue of court orders obtained by the Child and Family Agency and the HSE, which have deemed him a danger to himself and to others since 2011, when he was aged just 14.

Initially, he was held in Ireland, but it quickly became apparent that there were no suitable services available for him here.

So the High Court in Dublin ordered that he be sent to a secure mental health facility in England instead.

The average period an adolescent would be held in a special care unit in Ireland is between six and nine months.

Usually by that stage their behaviour would have stabilised to the extent where they could be moved to a less secure facility, a foster placement, or their family home.

But details are now emerging which show that Irish teens sent to the UK for detention and treatment can end up staying there for years, such is the seriousness of their conditions.

PA is now 18 and has been at the secure facility in England since October 2011.

He has been diagnosed with manic depression and a severe personality disorder.

When he reached the age of majority earlier this year, he was not been able to successfully challenge is detention.

The emergence of details about such cases is rare.

Currently there are five children and at least three adults being detained abroad in secure care facilities in the same way as PA because the State does not have the capacity to help them in Ireland.

The average cost of such care is €7,000-per week per patient.

Their detentions are reviewed on a continual basis by the High Court in Dublin.

In the case of placements in the UK, the family division of the High Court in London also considers the facts of each case.

Although health authorities have invested millions of euro building extra facilities for deeply troubled teens, they say that even when these come on stream next year there will still be cases that require placement abroad.

Such cases don’t get much attention in the media and to a certain extent the people involved have become Ireland’s forgotten children.

We know more about PA’s situation than many of the other cases as a result of a reserved judgment handed down by London’s High Court earlier this month.

That court was reviewing the detention of three young Irish people, each of whom is being held at UK facilities on foot of orders obtained by the HSE.

In each case, Mr Justice Jonathan Baker found there were no grounds for the British courts not to recognise the care orders made by the Irish High Court.

Each of the cases was harrowing in its own right, but PA’s was particularly so.

He had what the court described as “an extremely troubled childhood” and ended up in foster care at the age of 13.

However, foster placements broke down on no less than 20 occasions due to his challenging behaviour.

He was taken into care by the HSE due to “escalating problematic behaviour and criminal activity”.

The HSE decided to seek treatment for him abroad shortly after he told Irish care unit staff “he was bored of assaulting people and would like to see someone murdered”.

He was initially sent to a secure facility in Scotland, but staff there felt unable to work with him as a result of his levels of aggression and he ended up at a facility in England.

At one point he was considered so aggressive that he had to be secured in a separate ward with three nursing staff with him at all times.

Things have improved for him since the riot police and escape episodes and he finally began responding to treatment last year.

He was able to return to Ireland last October for a High Court review of his detention and also got to visit his family home for the first time in years.

There is still no sign of him being allowed to return here on a permanent basis.

A psychiatrist responsible for mental health services in the area where PA is from testified there were no facilities in the Republic of Ireland that could replicate those available in the English facility.

Another psychiatrist, based in England, certified that PA had the capacity to bring litigation challenging his detention after he turned 18 earlier this year.

However, at the High Court in Dublin, Ms Justice Bronagh O’Hanlon found he lacked the capacity to make material decisions on his treatment and therapy.

A second Irish man, aged 20, also had his case reviewed by the London High Court.

He was sent to the same facility as PA in late 2012 and earlier this year was moved to a lower security unit elsewhere in England.

He has had a history of ADHD, substance misuse, conduct disorders and aggressive, as well as unpredictable behaviour deemed to put himself and others at risk.

The court heard he had exhibited sexualised behaviour in public and in private on a number of occasions.

Unlike PA, he had not sought to have his detention reviewed, but the court felt it necessary to assess his case anyway.

It decided there was no reason not to recognise the detention orders made by the High Court in Dublin.

A similar finding was made by Mr Justice Baker in the case of an 18-year-old woman, known by the initials PB.

She has been in an English mental health facility since late 2013 and although the High Court directed she should be moved to a facility in the west of Ireland not later than June 12 this year, this did not happen.

The young woman first came to the attention of mental health services in Ireland in December 2011 after a failed suicide attempt.

According to Mr Justice Baker’s ruling, there was evidence she may have been abused by a member of her family.

Similar to PA’s case, clinicians have testified there are no facilities in Ireland to meet her needs.

In November last year she returned to Ireland for a visit as part of a planned attempt to enable her to return home. Unfortunately, this proved disastrous.

Her mental state deteriorated after returning to the English facility and she made a number of suicide attempts.

Earlier this week she testified via video link to the High Court in Dublin, stating the “most important thing is to be returned back to my country”.

The hearing was called after the HSE sought a change to the High Court direction that she be returned to Ireland this month.

The HSE is now seeking to vary this order to keep her in treatment in the UK, believing she remains a high suicide risk and would be safer there.

She told Mr Justice Seamus Noonan she would not take her own life and had many plans for the future, including attending university and running marathon.

The young woman said she thought about Ireland “every moment of every day”.

She misses her family and friends and even “silly things” like Supermacs, fields and cows.

When she was told the HSE would seek to stop her returning home this month, she said she felt “hopeless” and believed her mental health would “really deteriorate” if she remained in the UK.

She said she would agree to undergo voluntary treatment at a hospital in Ireland if returned.

The court heard she was currently sharing a locked ward with 12 other girls and that staff were constantly present.

She is no longer a high security patient, but during her testimony she gave an insight into conditions for such patients.

They cannot have access to the gardens, are not permitted to wear shoes and must wear just one layer of clothing.

They are also not allowed to watch television and are under constant one on one observation, she said.

Mr Justice Noonan remarked during the hearing that it was not clear to him why she could not be kept safely here.

The court also heard how the young woman has written a letter to Health Minister Leo Varadkar and a poignant poem to the HSE, appealing for her return.

The poem included the lines: “If there’s truly no service, put a bespoke one in place.

“Stop hesitating, because it’s a disgrace.

“My mood hasn’t deteriorated and my suicide risk hasn’t increased.

“I’m only 18. I don’t want to be pronounced deceased.

“Just give me a chance to prove all that I have to give.

“I have my whole life ahead of me yet to live.”

The court is due to hear further details of her case this week.

The core issue it must decide upon is the young woman’s capacity to make decisions about her treatment.